A rather common name for running clubs in Great Britain. But, more generally known, a running game that such clubs played. It was originally played by schoolboys in the early 1800's, but gained popularity as a fitness activity amongst adults later.
To start the game, two "hares" are chosen, usually for their speed and knowledge of the surrounding area. The rest of the participants are "hounds". The hares are given a 15-20 minute head start, running in any direction they see fit, together. They carry between them a bag of "scent," which is either some varied mixture of chalk and bits of paper.
As the hares run, they drop bits of the scent along their path, enough to vaguely leave a trail, but not too obviously. They also should make plenty of false trails. This will buy them some time, because after their head start is up, the hounds are free to go after the hares. Leaving a false trail is their best defense.
The game ends when either the hares are caught, or else they feel that their trail is long enough, and return to the starting point (marking the trail the whole way, of course).
A modern version of the game is referred to as hashing, but this version is not recommended as a children's game, due to the amount of alcohol consumed.